Decision: should I start with BuddyPress or start more simply if I can?

Here's a question for the website strategists out there:

I am building a community for entrepreneurs and can see that the future will require robust BuddyPress/MultiSite functionality. But I want to start much more simply, mostly with just knowledge, tips, and forums, etc. I keep finding plugins that adequately provide "lite" community features that will be fine for the first year or so. So my question is, how important is it that I install BuddyPress from the get-go so that profiles are set up correctly and the right hooks and things are there to enable all of the future things I want to do... Or is it ok that I start with a simpler site with the basics that do not require BuddyPress/MU (which is what I would prefer)? Would I be making a big mistake doing this when I already know that eventually I definitely want to use BuddyPress/MU? Would I be creating a nightmare for myself, or would it be relatively painless to migrate/upgrade? Or maybe the answer would be to completely redo the site on BuddyPress/MU once we have enough subscribers to make a community... but then I think I lose all of the conversations, etc.

Sam